Custom HTTP library with ajax (Practice)

app.js

let instance = new azHTTPLibrary;

// GET
// instance.get('https://jsonplaceholder.typicode.com/posts', function(err, response){
//   if(err){
//     console.log(response);
//   } else {
//     console.log('Get post...');
//     console.log(response);
//   }
// });

// // POST
// instance.post('https://jsonplaceholder.typicode.com/posts', {title: 'custom post', body: 'Custom body'}, function(err, response){
//   console.log('Inserting post');
//   console.log(response);
// });

// // PUT
// instance.put('https://jsonplaceholder.typicode.com/posts/5', {title: 'custom post 5', body: 'Custom body'}, function(err, response){
//   console.log('Updating post');
//   console.log(response);
// });

// DELETE
instance.delete('https://jsonplaceholder.typicode.com/posts/5', function(err, response){
  console.log('Deleting post');
  console.log(response);
});

azHTTPLibrary.js

function azHTTPLibrary(){
    this.http = new XMLHttpRequest();
}

// Make GET request
azHTTPLibrary.prototype.get = function(url, cb){
    this.http.open('GET', url, true);

    // let self = this;
    // this.http.onload = function(){
    //     if(self.http.status === 200){
    //         console.log(self.http.responseText);
    //     }
    // };

    // without "self"
    this.http.onload = function(){
        if(this.status === 200){
            cb(null, this.responseText);
        } else {
            cb(this.status, "Error:" + this.status);
        }
    };

    this.http.send();
}

// Make POST request
azHTTPLibrary.prototype.post = function(url, post, cb){
    this.http.open('POST', url, true);
    this.http.setRequestHeader('Content-Type', 'application/json');

    this.http.onload = function(){
        cb(null, this.responseText);
    }

    this.http.send(JSON.stringify(post));
}

// Make PUT request
azHTTPLibrary.prototype.put = function(url, newContnet, cb){
    this.http.open('PUT', url, true);
    this.http.setRequestHeader('Content-Type', 'application/json');

    this.http.onload = function(){
        cb(null, this.responseText);
    }

    this.http.send(JSON.stringify(newContnet));
}

// Make DELETE request
azHTTPLibrary.prototype.delete = function(url, cb){
    this.http.open('DELETE', url, true);

    this.http.onload = function(){
        if(this.status === 200){
            cb(null, 'Deleted post');
        } else {
            cb(this.status, "Error:" + this.status);
        }
    };

    this.http.send();
}